. Fibrolase is a direct acting fibrinolytic metalloprotease found in southern copperhead snake venom which cleaves fibrin independently of plasmin (ogen). As such, it does not generate plasmin and therefore, is not inactivated by either plasminogen activator inhibitor or alpha 2 antiplasmin. Fibrolase lyses fibrin by cleaving several Leu-Lys bonds in the alpha and beta chains, a major one being Leu413-Lys414 in the alpha chain. The fibrinolytic actions of fibrolase have been demonstrated in arterial and venous animal models of thrombosis. It does not activate platelets or coagulation, nor does it lyse red blood cells. The second objective is to determine the stoichiometry and kinetics of interactions of fibrolase and its chimeric derivative with alpha 2-macroglobulin the major endogenous inhibitor of fibrolase. The third aim is to develop a fluorescent assay for fibrolase.